Conference turris::fortran

1214.0. "UNIX data file slightly different from VMS data file, same code" by PEACHS::DALEY (Maybe I should drink more coffee...or less!) Thu Mar 06 1997 15:05

Hi,

Explaination first, sample code at the end.

Customer writes a value (unformatted) to a file in a fortran program on 
unix.  ftp's or copies that file to VMS, and the same program there
can't read the data.  He notices two things:

- The same data written on VMS has a different hex value in the files.

- If he ftp's the file over from unix, the values are transposed 
  little/big endian stuff, I suppose.  That's for another conference.  

The question for this conference is:  Why are the values different in the
two files, and does it matter?  For instance, the value written for 
.98675 on unix dumps out like this:

	od -h xxx.fil
	0000000  9ba6 3f7c
	0000004

But on VMS, the file written looks like this:

     Dump of file $1$DUA1:[DALEY]XXX.FIL;2 on  6-MAR-1997 14:41:04.84
     File ID (2415,1,0)   End of file block 1 / Allocated 3

     Record number 1 (00000001), 4 (0004) bytes, RFA(0001,0000,0000)

                                 9BA6407C |@�............. 000000

3f7c becomes 407c.  Why is that?  

Any insight is appreciated.

Regards,

John


Here's the sample program:

      program xxx
      implicit none
      structure       /stats/
        union
          map
              real*4          null_time
          end map
        end union
      end structure
      record /stats/ stats_rec

      open (  access = 'sequential',
     1                       carriagecontrol = 'list',
     1                       dispose = 'save',
     1                       file = 'xxx.fil',
     1                       status = 'new',
     1                       unit = 6,
     1                       shared,
     1                       recordtype='fixed',
     1                       form='unformatted',
     1                       recl=1 )
      stats_rec.null_time = .98675
      write (unit=6) stats_rec
      close ( unit=6, dispose='save' )
      end

Different datatypes.  VMS uses F_float as the default for real*4, UNIX uses
IEEE.  On Alpha, you can compile /FLOAT=IEEE to make it be the same.  On VAX,
it's a bit tougher because you used a RECORD - if you had just used a
regular variable, or a record field, you could open with 
CONVERT='LITTLE_ENDIAN'.

$ fort/float=ieee t
$ link t
$ run t
$ dump xxx.fil

Dump of file USER_DISK:[LIONEL]XXX.FIL;1 on  6-MAR-1997 15:09:31.97
File ID (17343,22,0)   End of file block 1 / Allocated 4

Virtual block number 1 (00000001), 512 (0200) bytes

 00000000 00000000 00000000 3F7C9BA6 �.|?............ 000000

Note that because you used od -h on UNIX, it dumps in word order.

			Steve